Knee braces are widely used to stabilize and protect the knee joint. For example, knee braces are often used to prevent damage to the anterior cruciate ligament, posterior cruciate ligament, medial collateral ligament, lateral collateral ligament and/or meniscus in a knee joint. Knee braces are particularly useful to protect the knee joint during vigorous athletic activities such as running, basketball, football and skiing, and they are also used to stabilize the knee joint during recovery or rehabilitation from surgery or an injury.
A knee brace typically includes an upper frame, a lower frame, and a hinge connecting the upper frame to the lower frame. The upper frame often has straps that wrap around the quadriceps or hamstring, and the lower frame often has straps that wrap around the calf. Each portion of the frame is configured to fit the shape of the corresponding portion of the leg. The hinge allows the lower frame to pivot relative to the upper frame as the knee bends. Many braces have a hinge on each side of the knee joint to give the brace additional strength.
Conventional hinges for knee braces include a single axis pivot, two gears and a four-bar linkage. The conventional geared hinge mechanisms typically have two rotating gears with interlocking teeth. The single axis pivot and geared hinge mechanisms have several disadvantages. First, the single axis pivot and geared hinge mechanisms limit the range of flexion of the leg. Second, the single axis pivot and geared hinges do not simulate the natural movement of the knee joint when the leg bends or extends. The motion of the human knee joint is quite complex and does not rotate uniformly from extension to flexion. Because the single axis pivot and geared hinge mechanisms cannot simulate the natural movement of the knee joint, the knee brace may force the knee into an unnatural position at extension or flexion if the straps on the knee brace are tight. This coupled with forces induced during activity may injure the knee joint. Moreover, a user may loosen the straps to avoid the discomfort resulting from the unnatural movement of the knee joint. If the straps on the knee brace are loose, however, the knee brace will slide down the leg during an activity. Such movement of the knee brace during an activity is uncomfortable and annoying. Additionally, as the knee brace slides down the leg, the straps might not be tight enough to provide the necessary support to the knee.
A four-bar linkage hinge mechanism better simulates the motion of the knee during flexion and extension than geared hinges. Four-bar linkage hinges, however, have several disadvantages. First, the motion of a four-bar linkage hinge is complex, making it difficult to set and adjust stops that limit the range of motion of the knee brace. As a result, patients may not accurately limit the range of motion with four-bar linkage hinge mechanisms. Second, four-bar linkage hinges are bigger than many other types of hinges. A big knee brace hinge can make it more difficult to pull clothes over the brace, and large hinges may interfere with the other knee joint during activities. Therefore, four-bar linkage hinges are not widely used in knee braces.